PM / sleep: Introduce command line argument for sleep state enumeration

On some systems the platform doesn't support neither
PM_SUSPEND_MEM nor PM_SUSPEND_STANDBY, so PM_SUSPEND_FREEZE is the
only available system sleep state.  However, some user space frameworks
only use the "mem" and (sometimes) "standby" sleep state labels, so
the users of those systems need to modify user space in order to be
able to use system suspend at all and that is not always possible.

For this reason, add a new kernel command line argument,
relative_sleep_states, allowing the users of those systems to change
the way in which the kernel assigns labels to system sleep states.
Namely, for relative_sleep_states=1, the "mem", "standby" and "freeze"
labels will enumerate the available system sleem states from the
deepest to the shallowest, respectively, so that "mem" is always
present in /sys/power/state and the other state strings may or may
not be presend depending on what is supported by the platform.

Update system sleep states documentation to reflect this change.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 20 insertions, 9 deletions

diff --git a/Documentation/ABI/testing/sysfs-power b/Documentation/ABI/testing/sysfs-power
index 64c9276..f455181 100644
--- a/Documentation/ABI/testing/sysfs-power
+++ b/Documentation/ABI/testing/sysfs-power
@@ -7,19 +7,30 @@ Description:
 		subsystem.
 
 What:		/sys/power/state
-Date:		August 2006
+Date:		May 2014
 Contact:	Rafael J. Wysocki <rjw@rjwysocki.net>
 Description:
-		The /sys/power/state file controls the system power state.
-		Reading from this file returns what states are supported,
-		which is hard-coded to 'freeze' (Low-Power Idle), 'standby'
-		(Power-On Suspend), 'mem' (Suspend-to-RAM), and 'disk'
-		(Suspend-to-Disk).
+		The /sys/power/state file controls system sleep states.
+		Reading from this file returns the available sleep state
+		labels, which may be "mem", "standby", "freeze" and "disk"
+		(hibernation).  The meanings of the first three labels depend on
+		the relative_sleep_states command line argument as follows:
+		 1) relative_sleep_states = 1
+		    "mem", "standby", "freeze" represent non-hibernation sleep
+		    states from the deepest ("mem", always present) to the
+		    shallowest ("freeze").  "standby" and "freeze" may or may
+		    not be present depending on the capabilities of the
+		    platform.  "freeze" can only be present if "standby" is
+		    present.
+		 2) relative_sleep_states = 0 (default)
+		    "mem" - "suspend-to-RAM", present if supported.
+		    "standby" - "power-on suspend", present if supported.
+		    "freeze" - "suspend-to-idle", always present.
 
 		Writing to this file one of these strings causes the system to
-		transition into that state. Please see the file
-		Documentation/power/states.txt for a description of each of
-		these states.
+		transition into the corresponding state, if available.  See
+		Documentation/power/states.txt for a description of what
+		"suspend-to-RAM", "power-on suspend" and "suspend-to-idle" mean.
 
 What:		/sys/power/disk
 Date:		September 2006